The escalating problem of bacterial resistance to antibiotics calls for radical changes in the existing antibacterial therapies. One of the most promising approaches is the use of antibiotic potentiators, compounds that make bacterial cells hypersusceptible to antibiotics. The goal of the project is to identify multiple novel molecular targets for potentiators. This will be accomplished by isolating antibiotic hypersusceptibility mutations of Gram-negative bacteria, Acinetobacter and/or Escherichia coli. These mutations will specify bacterial proteins whose inhibition is likely to potentiate antimicrobial action of antibiotics. Antibiotic hypersusceptibility is a very difficult phenotype to select, and only few such mutations are known. We have designed and tested a novel genetic strategy for selection of hypersusceptibility mutations, termed SDR. Application of this strategy will identify multiple mutations increasing bacterial susceptibility to beta-lactams (ampicillin, ceftazidime, imipenem), translational inhibitors (erythromycin, linezolid, tetracycline, and chloramphenicol) and fluoroquinolone antibiotics (ciprofloxacin). The molecular mechanisms underlying the effects of the most interesting of these mutations will be analyzed. In addition to identifying promising targets for potentiators, the project will help unravel new aspects of the mechanism of action of antibiotics and new features of bacterial physiology.